linux-kernel - Re: [PATCH] memcg: skip cgroup_file_notify if spinning is not allowed

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Message-ID: <aLtY6JqoOTMA-OtG@google.com>
Date: Fri, 5 Sep 2025 21:40:56 +0000
From: Peilin Ye <yepeilin@...gle.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Tejun Heo <tj@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>,
	Alexei Starovoitov <ast@...nel.org>,
	Kumar Kartikeya Dwivedi <memxor@...il.com>, bpf@...r.kernel.org,
	linux-mm@...ck.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH] memcg: skip cgroup_file_notify if spinning is not allowed

On Fri, Sep 05, 2025 at 02:33:16PM -0700, Shakeel Butt wrote:
> On Fri, Sep 05, 2025 at 08:48:46PM +0000, Peilin Ye wrote:
> > On Fri, Sep 05, 2025 at 01:16:06PM -0700, Shakeel Butt wrote:
> > > Generally memcg charging is allowed from all the contexts including NMI
> > > where even spinning on spinlock can cause locking issues. However one
> > > call chain was missed during the addition of memcg charging from any
> > > context support. That is try_charge_memcg() -> memcg_memory_event() ->
> > > cgroup_file_notify().
> > > 
> > > The possible function call tree under cgroup_file_notify() can acquire
> > > many different spin locks in spinning mode. Some of them are
> > > cgroup_file_kn_lock, kernfs_notify_lock, pool_workqeue's lock. So, let's
> > > just skip cgroup_file_notify() from memcg charging if the context does
> > > not allow spinning.
> > > 
> > > Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>
> > 
> > Tested-by: Peilin Ye <yepeilin@...gle.com>
> 
> Thanks Peilin. When you post the official patch for __GFP_HIGH in
> __bpf_async_init(), please add a comment on why __GFP_HIGH is used
> instead of GFP_ATOMIC.

Got it!  I'll schedule to have that done today.

Thanks,
Peilin Ye